Canon made a few different variants of their popular FD mount during its ~20-year production run. Here, Connor goes over the various differences in mounting mechanisms, coatings, and technology that you'll see.
Time Codes:
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00:00 - Introduction
00:25 - Mounting: Breech-Lock
01:08 - Mounting: New FD
01:58 - Coatings: S.C vs. S.S.C
02:31 - Coatings: New FD
02:47 - Conclusion